This invention is directed to a crossed-field switch device in which the geometry of the magnetic field and the electrodes is such that the active region in which glow mode discharge occurs is in a noncircular path.
The original Penning work on glow mode discharge in an interelectrode space where the magnetic field is at an angle to the electric field evolved to the structure of U.S. Pat. No. 2,182,736. A considerable amount of recent development work has been done at the Research Laboratories of Hughes Aircraft Company to develop a device having crossed-field low pressure glow mode discharge into a switch device which is capable of off-switching large current against high voltage. The off-switching speed is so rapid that off-switching can occur between the natural current zeroes of the usual 60 Hertz power line. While the off-switching device is very important for direct current off-switching, it is also applicable to rapid off-switching of power line alternating current between natural current zeroes. General background along these lines is illustrated in G. A. G. Hofmann U.S. Pat. No. 3,604,977 as well as in H. E. Gallagher and W. Knauer U.S. Pat. No. 3,963,960.
In order to maintain a glow discharge in an interelectrode space, the path of an electron as it moves from one electrode to another through the gas in the interelectrode region must be sufficiently long that cascading ionization occurs. In other words, statistically each electron must have enough collisions to produce more than one ionizing collision. The maintenance of gas pressure and the lengthening of the effective electron path between the electrodes by the application of the crossed magnetic field is discussed in G. A. G. Hoffmann and R. C. Knechtli U.S. Pat. No. 3,558,960; M. A. Lutz and R. C. Knechtli U.S. Pat. No. 3,638,061; R. E. Lund and G. A. G. Hofmann U.S. Pat. No. 3,641,384; and G. A. G. Hofmann U.S. Pat. No. 3,769,537. Each of these patents shows the Paschen curve of voltage vs. the product pd where p is pressure and d is the dimension of the interelectrode space. These curves are for a particular gas and zero magnetic field. The curves define regions between conductive and nonconductive conditions. They show that for a particular value of the product pd, the voltage at which breakdown into the glow mode occurs is at a minimum.
M. A. Lutz and G. A. G. Hofmann U.S. Pat. No. 3,678,289 discusses off-switching and discusses the characteristics of the glow mode discharge which permit off-switching. The patent shows in FIG. 3 a curve of the applied voltage across the interelectrode space vs. the magnetic field in the interelectrode space and shows the relationships of these parameters in which glow mode discharge does and does not occur, for fixed values of the product pd and for a particular gas.
It is apparent in these structures that the anode and cathode electrodes are of cylindrical nature and lie on a common axis to provide a cylindrical interelectrode space of substantially constant spacing d. This configuration evolved both because of the mechanical reasons of convenience in forming electrodes as surfaces of revolution around their axes and the desirability of cylindrical structure as pressure vessels, because the cathode electrode or its housing must withstand substantially atmospheric pressure. In addition, the designers of such equipment felt that the active plasma region or discharge path in addition to being continuous must also be a smooth circular curve to maintain the glow discharge characteristics in the active region. These design criteria limit the amount of effective electrode area because of the difficulty of constructing very large cylindrical structures with the electrodes accurately spaced. These problems are overcome by the invention of the present asymmetric crossed-field switch device and the discovery that the active region glow discharge continuous path need not be circular.